The present invention relates to a radiotelephone arranged for transmitting or receiving signals in a first or second frequency band, comprising a first antenna and filter system intended to ensure the transmission or reception of signals in the first frequency band, a second antenna and filter system intended to ensure the transmission or reception of signals in the second frequency band, and a selection device for selecting the frequency band used and a frequency management device controlling said selection device, in which radiotelephone a frequency conversion from either frequency band to an intermediate frequency is realized by a single local oscillator and a single mixer.
A radiotelephone capable of operating with two types of transmission systems which have different characteristic features, for example, the GSM and DECT features, has already been proposed. In the document EP-A-653851 it is indicated that in this case an intermediate frequency could be advantageously selected as being substantially equal to half the frequency difference between the two frequency bands. Such a telephone requires only a single local oscillator and also a single mixer which then, on the basis of a center frequency between the two bands effect a change by a lower value from the highest transmission/receiving frequency and by a higher value from the lowest transmission/receiving frequency. Thus the doubling of certain functions of the telephone is avoided, which renders the telephone less expensive.
Other functions have thus far been considered hard to share by the two transmission systems, because these functions are strictly linked to the frequency they are subjected to.